Secondary batteries capable of charging/discharging have been used widely as energy sources for wireless mobile devices. In addition, secondary batteries have been given many attentions as power sources for electric vehicles (EV) and hybrid electric vehicles (HEV) suggested as solutions for overcoming air pollution caused by general gasoline vehicles and diesel vehicles using fossil fuel.
Since middle- and large-size devices such as vehicles require high-output large-capacity power sources, a battery module having a plurality of battery cells electrically connected with each other and a middle- and large-size battery pack including the same as a unit module are used. Such a battery module and a battery pack are provided with a small size and low weight preferably, and thus a prismatic battery and pouch-type battery, which can be stacked with high density and have a low weight as compared to capacity, are used mainly as a unit cell for a battery module. Particularly, since a pouch-type battery using an aluminum laminate sheet or the like as a case has a low weight, requires low manufacturing cost and allows easy deformation, it has been given many attentions.
Battery cells forming a battery module generates a large amount of heat during charging/discharging. Particularly, a laminate sheet of a pouch-type battery used widely for a high-output large-capacity battery module and battery pack is surface-coated with a polymer material having low thermal conductivity, and thus is not effective for cooling the temperature of the whole battery cell. When the heat of a battery module generated during charging/discharging is not removed effectively, heat accumulation occurs, resulting in deterioration of the battery module. In some cases, this causes ignition or explosion of the battery module. Therefore, a cooling member is required essentially for cooling the battery cells embedded in such a high-output large-capacity battery module and a battery pack including the same.
In general, a battery module is manufactured by stacking a plurality of battery cells with high density and the adjacent battery cells are spaced apart from each other by a predetermined interval in order to remove the heat generated during charging/discharging. For example, battery cells are spaced apart from each other by a predetermined interval and stacked successively without any additional members. Otherwise, in the case of battery cells having low mechanical rigidity, one or a combination of at least two battery cells are embedded in a cartridge and then a plurality of such cartridges are stacked to provide a battery module.
In order to remove the heat accumulated in such stacked battery cells effectively, a heat transfer member that is in thermal contact with the battery cells, and a water cooling type or air cooling type cooling unit configured to remove the heat absorbed by the heat transfer member are used. The heat transfer member is a heat bridge by which the batteries are connected with the cooling unit and transfers the heat to the cooling unit so that the temperature of the battery cells may be reduced. A typical example of the heat transfer member is a metal-only cooling plate having high thermal conductivity.
FIG. 1 shows a cooling plate applied to a conventional battery module.
As shown in FIG. 1, the cooling plate 20 is provided so that it may be in thermal contact with the stacked cells 10. Thus, heat transfer is carried out from the battery cells 10 to the cooling plate 20, and the heat transferred to the cooling plate 20 is removed by a cooling unit (not shown). The conventional cooling plate 20 is generally manufactured by using an aluminum (Al) material.
Meanwhile, as mentioned above, a battery module and a battery pack are provided preferably with a small size and low weight. Thus, it is required to reduce not only the weight of a battery cell itself but also the weight of a part such as a heat transfer member or cooling unit configured to cooling the battery cell. However, the conventional cooling plate made of aluminum causes an increase in weight due to aluminum. Therefore, it is required to improve this in view of weight reduction of a battery module.